The invention relates to a thread carrying apparatus and to a textile machine, in particular to a weaving machine, which includes a thread carrying apparatus which reduces the frictional force between the thread and the thread carrying apparatus.
Components in machines of all kinds which are in contact with rapidly moved threads, with the threads also frequently being pressed against the corresponding component with great force, are subject to special stresses through frictional forces. In this the negative influences of course affect not only the components which carry the threads, but in particular also the threads themselves, which also suffer as a result of the frictional forces.
In the context of this application, components of machines of all kinds which are in contact with threads are designated as thread carrying elements. In this context the threads can be temporarily or permanently guided over or at a surface of the thread carrying element or lie in contact at a surface of the thread carrying element in the operating state. In this context the term thread shall in the following include in particular textile threads, especially also threads in the form of little bands, including, for example, wool, cotton or silk, or yarns or twines such as e.g. paper yarns, celluloid yarns or synthetic yarns of perlon, nylon, dralon or other synthetic materials, as well as threads in the broadest sense of the word, that is, for example, also threads of glass, metal or other materials.
A category of machines which is important in practice and which has a large number of thread carrying elements of the most diverse kinds is textile machines in the broadest sense of the word and thus in particular weaving machines in the most varied embodiments. In these machines, threads are guided by thread carrying elements, partly at extremely high speeds and in the presence of strong pressing forces. In this connection the thread carrying elements can for example be arranged as simple deflection elements, such as deflection rollers, which can either be arranged to be stationary or to be rotatable about an axis, or can be designed as eyes through which the thread passes. Moreover, a thread carrying element can however for example also be a drum store of a weaving machine or a thread supply device of a knitting machine, or a thread guiding element of a weaving rotor of a multiple-phase weaving machine. Of course, as already mentioned, the term thread carrying element is not intended in the context of this invention to be restricted to the above-described examples, and also not to textile machines.
Particularly strong frictional forces arise at points at which the thread is guided at or over the thread carrying element at high speed. In this, considerable heat development can then occur locally, which can lead to intolerable temperature increases and/or to temperature gradients in the material of the thread carrying element itself and in further neighboring system components. In particular the thread can be damaged in the process which, for example in the case of weaving, can lead to the weaving product having a clearly poor quality. A further problem is often the aggressive abrasive behavior of the thread in cooperation with the discussed frictional effects, which can lead among other things to a premature wear of the thread carrying element. This is a problem which is well known for example in thread guiding elements of weaving rotors of multiple-phase weaving machines and plays a considerable role there. Thus in this kind of weaving machine the friction at the thread guiding elements is an essential parameter for the performance of these machines. The friction which the thread experiences during its passage at the numerous deflection points at the thread guiding elements is one of the most important performance limiting factors in multiple-phase weaving machines. Moreover, frictional effects impair the quality of the weaving products and restrict the article spectrum of the machine.
Moreover, in thread carrying elements against which the thread is not pressed with a great force and in which the heat development remains within bounds, such as for example in a thread drum of a drum store of a weaving machine, the friction between the thread and the thread carrying element can have a clearly negative influence on the operation of the machine. In the operation of weaving machines for example in the processing of weft yarns, in particular of weft yarns in the form of little bands, which tend to stick to the thread carrying elements, it has been shown that the friction at the thread carrying elements which respectively carry or guide the weft yarn plays an important role. In this the sticking of the thread to the thread carrying element is frequently also enhanced by substances which are carried along by the thread such as oil, wax, size or other substances.
In studies of the operating behavior of weaving machines it was found in particular that a reduction of the friction can contribute to significantly increasing the presently existing limit of the weft insertion performance. In this a particular significance is accorded to the thread storage of the weaving machine with respect to the influence of the friction in the drawing off of the weft thread during the weft insertion. The maximum speed with which the weft thread can be inserted into the shed is limited, not least by the level of the friction between the weft thread and the thread drum during the drawing off of the weft thread from the thread drum. Moreover, additional tensile forces arise of course in the weft thread as a result of the friction (between the thread drum and the weft thread) which stress the thread, which, in particular in fine fabrics or, in the case of weft threads which are plastically or elastically deformable under certain tensile loadings, can quite noticeably negatively influence the quality of the woven product.
Different ideas are known for reducing the friction at thread carrying elements. For example the wear which is caused through friction mechanisms can be reduced by providing the thread carrying elements with particularly low-friction coatings, such as for example with ceramics, or by equipping the threads with friction reducing lubricants. Measures of this kind are admittedly often suitable for reducing the friction between the thread carrying element and the thread to a certain extent; a not insignificant portion of residual friction is, however, unavoidable. In addition a suitable processing or coating respectively of the frictional surfaces of the thread carrying elements does not lead to the desired success in all cases, and in particular the use of friction reducing lubricants can easily have a negative influence on certain thread carrying elements, such as for example on the drum store of a weaving machine, depending on the kind of the thread. Their use is also often prohibited for technical reasons.
An alternative idea for reducing the friction between the thread and the thread carrying element is presented for example in EP 1 126 063 A2, which proposes a friction purveyor or thread regulating wheel for a knitting machine which has a vibration producing unit which acts on the thread. In this the thread, which is supplied to a thread supply wheel which is rotationally fixedly connected to a drive shaft, is guided by a thread guiding element in the form of an eye, with the eye being connected to a device which sets the eye and thus the thread into oscillation. In this the eye which guides the thread executes, at each rotation of the thread supply wheel, an oscillatory movement of low amplitude, which is also transferred to the thread, through which the friction between the thread and the rotating thread supply wheel is reduced. In this the eye is mechanically connected to a rotating shaft of the knitting machine via an eccentric mechanism or is driven via an electromagnet which is supplied with a low frequency voltage.
Although a certain reduction of the frictional forces between the thread and the thread supply wheel can be achieved with the thread regulating wheel which is shown in EP 1 126 063 A2, this technique has considerable disadvantages and can be used elsewhere only with restrictions.
One of the serious disadvantages of this apparatus consists in that the eye must move the thread back and forth with a certain amplitude to transfer the vibration to the thread, which means that the source which excites the thread, that is, the eye, must execute a center-of-gravity movement as a whole. In this the force transmission in order to set the thread oscillating over a considerable length takes place quasi point-wise at the location at which the thread lies in contact at the eye. This has the consequence that the thread is continually charged with a considerable point-like tensile loading and with a considerable bending stress in the direction of the oscillatory movement of the eye, which is particularly disadvantageous. From this there of course also results a correspondingly large tensile stress in the direction of the thread. In very sensitive threads, in particular in threads of low breaking resistance, this method can hardly be used without damaging the thread and thus diminishing the quality of the finished product. Depending on the constitution of the thread the use can even be impossible. A further problem consists in that the oscillations are coupled in only at one point of the thread or at few points of the thread which are spaced from one another. This has the consequence that the thread is not uniformly loaded with the oscillations, since with increasing distance from the oscillating thread carrying eye the vibrations in the thread are increasingly more strongly damped. Through this the friction between the thread carrying element and the thread is not uniformly reduced when considered over the length of the thread, which can result in a non-uniform guiding of the thread, for example when drawing the thread off from a drum store. The result can be pulsating mechanical stresses in the thread, which can lead to an unacceptable reduction in quality of the product, for example during the insertion of a weft thread, in particular during the weaving of fine high quality cloths.
Since the charging of the thread with vibrations takes place in principle through a relatively high amplitude center-of-mass movement of a thread carrying element, for example through an oscillating eye through which the thread passes, the thread can be charged only with relatively low frequency vibrations, which are particularly easily transmitted to other system components of the machine. Moreover, the vibrations in the thread are already relatively highly damped down at a short distance from the point at which the oscillation is excited by the eye. Above all, however, for reasons of work protection legislation as well, such low frequency excitations in the audible range are more than precarious. Moreover, the above-discussed friction purveyor is mechanically very complicated and expensive and thus relatively susceptible to breakdown and is maintenance intensive.